With regard to 2023, if you have yet to establish a 401(k) plan you could look for one that includes a designated Roth account. I think that Vanguard has one. If you already have the Fidelity 401(k) plan then I don't think that you have that option for 2023 but could potentially move the 401(k) to another provider for 2024. Same for a SEP or SIMPLE plan. A SEP plan won't allow employee contributions, so that probably would not serve your needs.
Roth contributions for a SEP or SIMPLE plan were only recently introduced by the SECURE 2.0 Act and the IRS Has only just released guidance related to those. You would need to determine if your plan permits those.
